Two men behind New Zealand’s largest-ever methamphetamine importation operation have failed in their final attempt to overturn prison sentences of more than 20 years, after the country's supreme court dismissed their applications for leave to appeal.

Baltej Singh can now be revealed as the man who imported more than 700kg of meth.

Two men behind New Zealand’s largest-ever methamphetamine importation operation have failed in their final attempt to overturn prison sentences of more than 20 years, after the…